In recent years, the use of light-emitting diodes (LEDs) for various common lighting purposes has increased, and this trend has accelerated as advances have been made in LEDs and in LED-array bearing devices. Indeed, lighting needs which have primarily been served by fixtures using high-intensity discharge (HID) lamps, halogen lamps, compact florescent light (CFL) and other light sources are now increasingly beginning to be served by LEDs.
Light emitting diodes (LED or LEDs) are solid state devices that convert electric energy to light, and generally comprise one or more active layers of semiconductor material sandwiched between oppositely doped layers. Light is emitted from the active layer and from all surfaces of the LED. A typical high efficiency LED comprises an LED chip mounted to an LED package and encapsulated by a transparent medium. Many different types of LED die can be used individually or in combination in an LED package based on the package application. Possible die include DA, EZ, GaN, MB, RT, TR, UT, and XT LED die, commercially available from Cree, Inc. The efficient extraction of light from LEDs and the quality of that light are major concerns in LED package fabrication.
Some efforts have been made to develop small lenses for directing light emitted by small LED packages, and utilizing lenses intended to redirect some amount of emitted light to form a desired illumination pattern. However, such lenses have tended to fall short of the most highly desirable performance and uniformity of distribution of the LED-emitted light.
LEDs can be fabricated to emit light in various colors. However, conventional LEDs cannot generate white light from their active layers. In order to achieve white color, light from a blue emitting LED has been most commonly converted to white light by surrounding the LED with a yellow phosphor. The surrounding phosphor material “downconverts” the energy of some of the LED's blue light which increases the wavelength of the light, changing its color to yellow. While in such arrangements a large portion of the light is downconverted to yellow, some of the blue light still passes through the phosphor without being changed such that the resulting LED light has a cold-blue white color.
There have been efforts to manufacture white light which resembles the warm-yellow white color of light produced by the common non-LED light sources. Certain methods involve the use of LED packages including dies producing light of different colors which are mixed together to achieve the desirable yellow-white. Such methods require effective mixing of different color light, as well as efficient distribution of such light.
It would be highly beneficial to provide a lighting apparatus which produces a desired illumination with uniform distribution of the intended-color light.